Revision: 8/96 benzophenol, hydroxybenzene, C6H5OH; chloracetic acid, MCA,

Process Code: Navy and Marine Corps: ID-01-01/-99; Air Force: ST01; Army: DPT

Usage List: Navy: Medium; Marine Corps: Medium; Army: Low; Air Force: High

Substitute for: Chemical Paint Stripping CH2ClCOOH; methylene dichloride,

Applicable EPCRA Targeted Constituents: Toluene (CAS: 108-88-3), Xylenes (CAS: 1330-20-7), Methyl Ethyl Ketone (CAS: 78-93-3), Acetone (67-64-1), n-Butyl Alcohol (CAS: 71-36-3), Lead (CAS: 7439-92-1), Chromium (CAS: 7440-47-3), Zinc Compounds, Phenols (CAS: 108-95-2), Chloroacetic Acids (CAS: 79-11-8), Methylene Chloride (CAS: 75-09-2) Methyl benzene, phenylmethane, C6H5CH3; dimethylbenzene, C6H4(CH3)2; ethyl methyl

Overview:

Sodium bicarbonate stripping processes are used as alternatives to traditional chemical paint stripping. Bicarbonate of soda (or sodium bicarbonate) is a soft blast media with a heavier specific gravity and less hardness than most plastic abrasives. The bicarbonate of soda stripping process can be used with or without water. It is most frequently used with water, which acts as a dust suppressant. In this form, compressed air delivers sodium bicarbonate media from a pressure pot to a nozzle, where the media mixes with a stream of water. The soda/water mixture impacts the coated surface and removes old coatings from the substrate. The water used dissipates the heat generated by the abrasive process, reduces the amount of dust in the air, and assists in the paint removal by hydraulic action. Workers do not need to prewash or mask the surface of the material being stripped. The solid residue from the wastewater generated from this process can be separated by settling or filtration. butanol, butyric alcohol, CH3(CH2)2CH2OH;plumbum, Pb; Cr; carboxyic acid, phenylic acid,

The effectiveness of bicarbonate of soda stripping depends on optimizing a number of operating parameters, including nozzle pressure, standoff distance, angle of impingement, flow rate, water pressure, and traverse speed. In general, bicarbonate of soda stripping systems remove paint slower than most methods (other than chemical paint stripping) currently used. The type of equipment used in this stripping process may also have significantly different results (e.g. Aqua Miser® vs. the Accustrip System®). monochloroacetic acid, dichloromethane, CH2Cl2

Use of sodium bicarbonate in its dry form (or when not fully mixed with water) can create a cloud of dust that will require monitoring and may require containment to meet air standards. The dust generated is not an explosive hazard, nor is sodium bicarbonate toxic in this form. However, the airborne particulates generated from the stripping operation can contain toxic elements from the paint being removed This stripping process should be performed in areas where exhaust particulates can be contained and/or exhaust ventilation system controls are present to remove hazardous airborne metals. If bicarbonate of soda stripping is operated outdoors, air monitoring of dust (e.g. for metals) may be necessary to ensure that air standards are met. However, tests have shown that lead will adhere to the sodium bicarbonate, thus reducing the risk. Be sure to have your local Industrial Health Specialist check the air for any resident metals.

The waste generated from bicarbonate of soda stripping systems in the wet form is a wet slurry consisting of sodium bicarbonate media, water, paint chips, and miscellaneous residues such as dirt and grease. Some installations are employing centrifuges to separate the water from the contaminated waste stream, thus reducing the amount of hazardous waste being disposed. Filtered wastewater containing dissolved sodium bicarbonate may be treated at an industrial wastewater treatment plant. In its dry form, waste generated includes nuisance dust, paint chips, and miscellaneous residues such as dust and grease. The solid waste may be suitable for disposal in a sanitary landfill. Analysis of wastewater and waste solids is required prior to disposal. Wastewater and bicarbonate residue disposal requirements will depend on the toxicity of the coatings and pigments to be removed. The sodium bicarbonate media can not be recycled. The paint chip and miscellaneous residue wastes may be considered a hazardous waste.

Currently, bicarbonate of soda stripping is not approved by NAVAIR for depainting aircraft. NAVAIR's primary concern is that at temperatures of 140 to 160 degrees Fahrenheit, sodium bicarbonate may convert to sodium carbonate, which is corrosive.

This technology has been tested at the USMC Logistics Base, Albany, Georgia. They tested sodium bicarbonate media in three types of commercial off-the-shelf equipment. The cost of these systems ranged from $15,000 (Accustrip 16W) to $40,000 (Aqua Miser E25 and Jet Stripper DP-1). The Aqua Miser and Jet Stripper use medium-pressure water to remove paint with sodium bicarbonate injected to assist in removal effectiveness (with the Aqua Miser system, the sodium bicarbonate flow can be turned on and off as necessary). Accustrip uses a stream of 30 to 90 psi air and sodium bicarbonate, and is combined with a stream of blast water at the nozzle to try to eliminate the dust. In both cases, the sodium bicarbonate medium is then propelled against the surface, and the sharp edges of the media blast paint away from the base metal.

Materials Compatibility:

Material compatibility must be evaluated with respect to the item being cleaned. Uninhibited sodium bicarbonate and water residue can corrode substrates; however, current testing indicates that the corrosion potential of inhibited formulations is similar to that of organic solvent strippers. Results from an Air Force test program (Tasking Directive I-90) indicated that there was excessive corrosion of aluminum cladding materials when sodium bicarbonate and water slurry were used.

Safety and Health:

Health concerns are dependent on the variety of paint to be removed. Inhalation of lead- and zinc chromate-based paints can lead to irritation of the respiratory system. Some lead compounds are carcinogenic. Solvent-based paints can irritate the lungs and mucous membranes. Prolonged exposure can affect respiration and the central nervous system.

Because of the noise and dust produced (the amount of dust produced will vary from system to system), a sodium bicarbonate stripping system should only be operated in an isolated area outdoors or indoors in a confined or remote area. Operators must wear double hearing protection; an air-hood blast helmet with an air-supplied respirator and optional half mask (for those blasting systems that generate large amounts of dust), or a full-faced air purification respirator with HEPA filters; and protective clothing (e.g. rain suits, rubber gloves, and safety-toed rubber boots, depending upon the substrate coating).

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.

Benefits:

• Significant reduction in the amount of hazardous waste generated compared to chemical stripping
• Reduces the number of hours required for paint stripping in comparison to chemical stripping
• Selectively removes individual coating layers
• Prewashing and masking is not required in most applications
• No size limitations for parts being stripped
• Wastewater stream may be centrifuged to reduce its volume or treated (if required) at industrial wastewater treatment plants available to many installations
• Blast media is usually less expensive than PMB, wheat starch, and CO₂ pellets

Disadvantages:

• Requires subsequent washing of the item; thus, electrical components cannot be exposed to this stripping process
• The sodium bicarbonate solution can not be recycled for stripping, although the water can be separated for disposal
• May require monitoring
• Containment may be required
• Not approved by NAVAIR for depainting aircraft

Economic Analysis:

Annual operational costs for depainting 228 aircraft wheels with bicarbonate of soda stripping system (Accustrip) compared to chemical paint stripping were evaluated at the Lyndon B. Johnson Space Center, Houston, Texas, as shown below.

Assumptions:

• Accustrip System cost: $20,000
• Compressor, trailer mounted: $20,000
• Materials and installation: $125,000
• Other significant costs (engineering, contingency, startup): $60,000

	Bicarbonate of Soda Stripping	Chemical Stripping
Operational Costs:
Labor:	$2,200	$16,200
Material:	$2,600	$1,600
Waste Disposal:	$2,300	$41,200
Total Operational Costs:	$7,100	$59,000
Total Recovered Income:	$0	$0
Net Annual Cost/Benefit:	-$7,100	-$59,000

Economic Analysis Summary

Annual Savings for Bicarbonate of Soda Stripping System: $51,900

Capital Cost for Equipment/Process: $225,000

Payback Period for Investment in Equipment/Process: < 5 years

Approving Authority:

Navy: Approval has not been made by NAVAIR for application on aircraft and aircraft components without pretreatment of aircraft substrate to remove all blast media. This technology should be implemented only after engineering approval has been granted by cognizant authority.

Points of Contact:

Mike Seybold
Material Engineering Laboratory
Code 344
NADEP - Naval Air Station, North Island
San Diego, CA 92135
Phone: (619) 545-9663, DSN 735-9663

Talmon Perkins
JDMAG/MAT
Building 280, door 24
4170 Hebble Creek
Wright Patterson AFB, OH 45433-3653
Phone: (513) 476-2758, DSN: 986-2758, Fax: (513) 476-2233

Warren Akers
USMC Logistics Base
814 Radford Boulevard
Albany, GA 31704
Phone: (912) 439-5344, DSN 317-1126, Fax: (912) 439-6377

Mike Haas
San Antonio Air Logistics Center
SA-ALC/LAPSD
485 Quentin Roosevelt Road
Kelly AFB, TX 78241-5312
Phone: (210) 925-8541, DSN: 945-8541, Fax: (210) 925-7466

Scott Mauro
Naval Facilities Engineering Service Center, ESC 423
1100 23rd Avenue
Port Hueneme, CA 93043-4370
Phone: (805) 982-4889, DSN: 551-4889, Fax: (805) 982-4832

Vendors:

The following is a list of bicarbonate of soda stripping system manufacturers. This is not meant to be a complete list, as there may be other manufacturers of this type of equipment.

Aqua Miser®
Carolina Equipment and Supply
E. Larry Fulmer
7251 Cross Country Road
N. Charleston, SC 29418
Phone: (800) 394-4987 Ext. 20, Fax: (803) 760-3500

Accustrip System®
Schmidt Manufacturing, Inc.
P.O. Box 37
Fresno, TX 77545
Phone: (800) 231-2085 or (713) 431-1717, Fax: (713) 431-1717

JETSTRIPPER
WhiteMetal, Incorporated
6300 Midvale
Houston, TX 77087
Phone: (800) 728-8861

SOBI System
Friess Equipment
2222 Akron-Peninsula Road
Akron, OH 44313
Phone: (800) 899-7624, Fax: (216) 923-5833

ARMEX Blast Media
Church and Dwight Specialty Cleaning
469 N. Harrison Street
Princeton, NJ 08540
Phone: (800) 221-0453; Fax: (609) 497-7176

Source(s):

Joint Depot Maintenance Analysis Group, "Joint Paint Removal Study on Sodium Bicarbonate," February 1995.

Mr. Talmon Perkins, Joint Depot Maintenance Analysis Group, Wright Patterson AFB, May 1996.

Mr. Mike Seybold, Material Engineering Laboratory, NADEP, NAS North Island, San Diego, CA, April 1996.

Vendor communication, Mr. Chris Fulmer, Carolina Equipment and Supply Co., Inc., April 1996.

Vendor communication, Ms. Annette Rodriguez, Church and Dwight Co., Inc., April 1996.